DNA-based genealogy databases that offer ancestral matches based on your personal sample are expanding.
New technologies are allowing scientists to search for markers across the genome that can more precisely predict ancestry. Much of that data is being poured into public databases, supplying much more accurate and detailed information to genetic-testing companies and new consumer tests.
The basics of genetic ancestry testing are this: scientists search for genetic markers that appear more frequently in one population than in another. By combining the information gleaned from a number of markers--anywhere from tens to thousands--researchers can estimate the percentage of an individual's ancestry from different parent populations...
Now, both the scope and resolution of genomic ancestry studies are growing dramatically, thanks to specially designed microchips that allow scientists to quickly scan hundreds of thousands of spots on an individual's genome. That means that researchers can gather genetic information from more people in more places, generating better ancestry markers.
Although the testing still offers a probabilistic view of your ancestry; it tells where your ancestors are most likely from, not exactly who they are.
In the Star Trek: The Next Generation episode The Neutral Zone, counsellor Troi uses a genealogy computer to immediately display the family tree of someone who was revived after 400 years. The information for all of her descendants was displayed immediately.